Because of the proliferation of computers, word processing equipment, and a host of other data terminals installed at different locations within a building or community, techniques for communicating among them, without using the telephone company switching network, have been developed. Examples of such multiple access communication networks are described in U.S. Pat. Nos. 4,161,786; 4,089,584 and 4,210,780. All of these various systems typically include a transmission bus along which there are located a plurality of subscribers. The bus is organized in two, oppositely directed, unidirectional signal paths. One constitutes the "talk" path into which signals from the several subscriber station are launched. The other path constitutes the "listen" path from which the several subscribers receive signals. A central controller allocates the network resources, controlling access to the network and assigning time slots to the respective subscribers.
In view of the ever increasing number and variety of data terminals, the goals of any information distribution system for the foreseeable future must be twofold. First, the system must be designed to make efficient use of the facilities and equipment on hand. Second, it must be designed to permit efficient and graceful rearrangement and growth of the network as both the size of the network and the sophistication of the equipment served increase.